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Project Y Axis reversing when Z axis in motion

Discussion in 'CNC Projects' started by SteveeW, Jul 3, 2020.

  1. SteveeW

    SteveeW New
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    Anyone seen this before?
    I have a home built desktop CNC which I have been tinkering with for a few months now, I'm mainly using it for etching PCBs. A few days ago, I tried Candles' Height map feature and fund it was not following the G-Code path properly. Tried a few things and have concluded it's as the leveling feature moves the Z Axis to follow the surface of the PCB Y can sometimes invert.

    As it was following the same path every time, I tried some GCode directly and it is consistant.. if I move Z Down while attempting to move Y away, Y will in fact come forward.

    I;ve searched here and other places, I did find a tread which suggested it could be a fault with the board, so bought a new one.... EXACTLY the same.. Dono what to do next.

    Has anyone seen this before, and if so what can i do to stop it?
     
  2. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
    Staff Member Moderator Builder Resident Builder

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  3. SteveeW

    SteveeW New
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    Hi Peter, thanks for your input.

    That was my first thought, I have checked the wiring, but I ruled it out as unlikely as the Y axis uses 2 motors which are moving consistently in the wrong direction.

    If I move Z independently, it works fine it is only one combination which is causing the problem and its every time.

    GCode Result

    G01 F100 - Set feedrate - OK
    G91 - Set Relative movement
    G01 Y5 Z5 - Up Back
    G01 Y-5 Z5 - Forward Down
    G01 Y-5 Z-5 - Forward Down
    G01 Y5 Z-5 - Forward Down

    I hadn't realized, but there is actualy only one scenario where the Y axis will go back when also moving Z.. No less baffling....

    I have used 2 UNO boards, different types in fact and they both do the same.
     
  4. SteveeW

    SteveeW New
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    Ok... May have answered my own question looking the above results.
    It looks like there may be some cross connection on the direction pins of Z and Y..

    And sure enough tested with a Meter and there's only 10 ohms between them compared with 10Mohm between other Axis'

    Couldn't see anything, but ran a screwdriver between the solder joints between pins 6 and 7 on the CNC shield.. Short has gone.

    Everything back together... Bingo!

    Great site BTW
     
    Peter Van Der Walt likes this.

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